The present invention relates generally to the packaging of optoelectronic devices within a fiber optic transceiver for telecommunication and data communication applications.
The speed of computers and the data transfer between them is ever increasing. Optical data transmission techniques have been developed to provide high capacity signal transmission without many of the physical limitations for electrical cables. Fiber-optic cables have advantageous transmission characteristics, which are utilized with optoelectronic devices such as fiber-optic transceivers (FOT) by converting electrical signals into optical signals and vice versa at the ends of the fiber-optic cables.
The light beams utilized within an optical signal transmission have continuously extending bandwidths, which allow higher data transmission rates in the optical connection. As a result, more optoelectronic and electronic circuitry is necessary within the FOT to process the signal flow.
The typical hardware architecture of computers involves circuit boards that are perpendicularly connected with a pin edge or a pin array in lengthy multi-pin connectors, which are laterally arrayed on a mother board. That way, the circuit boards are oriented parallel with their receptacle end showing towards the back end of the computer. The designated ends have mounting sites that carry the cable connectors. The cable connectors typically reach through open slots in the back face of the computer chassis such that the communication cables can be connected from outside.
The distance between the open slots is standardized in the computer industry, which leaves a predetermined gap between the parallel oriented circuit boards.
The core of a FOT is typically a planar optoelectronic semiconductor (POS) that receives and emits the light beams perpendicular to its top surface. Since the fiber cable is connected normal to the computer back face as other communication cables, the POS must have a first distinct orientation, which is perpendicular oriented to the circuit board.
To focus the light beams, lenses are placed between the end of the fiber cable and the planar semiconductor. They too must be placed according to the first distinct orientation and are therefore preferably united in a subassembly.
The signals converted in the POS have to be processed within the transceiver. A secondary electronic circuitry (SEC) buffers, amplifies and filters signals that are provided to and derived from the POS.
A typical transceiver board of a FOT carries the sub assembly, the SEC and a pin array, which provides the mechanical and electrical connection of the whole FOT to the mounting site of the circuit board, to which it is soldered.
The size of the pin array(s) defines (together with the space demands for the SEC) the physical extension of the transceiver board, which is several times longer than the POS size. The sub-assembly is placed together with the individual components of the SEC on the transceiver board in a second building orientation.
Due to the continuing miniaturization of semiconductor devices the circuitry involved becomes smaller in size. At the same time more conductive traces and leads needs to be provided between and within the POS and the SEC. The higher complexity and density thereby raises the demand for novel packaging designs.
With higher signal transmission rates, the resistance and the capacitance in the conductive traces and leads become more influential and impose a certain latency upon the FOT. Therefore, there exists a need for a packaging that keeps the length of conductive traces and leads to a minimum.
The high circuit density and high signal processing rate in FOT""s result in a thermal load. FOT""s need to be designed in a way that the circuitry receives sufficient cooling.
The increased signal density and high bandwidth of the light beams become sensitive to attenuation and reflectance in the optical path. This occurs mainly where fiber optics are interrupted or when the beams have to pass through a number of optical elements. Therefore, there exists a need to keep the optical transitions within the FOT to a minimum.
Cable ends are typically held in cable connectors with support panels connected directly to the computer chassis. Excessive mechanical load and torque on the cable ends bear the risk of overcoming the stiffness of these support panels and imposing a deformation onto the FOT. The FOT needs to be designed to withstand a minimal deformation and maintain the alignment of the cable end with the lens system and the POS.
To extend the application of FOT for mass-produced, low-cost computers, the individual components need to be economical to fabricate, and the assembly of the FOT needs to be simple and reliable at the same time.
A number of attempts have been made to integrate the design needs as described above into a feasible packaging.
The most conventional FOT as it is known to those skilled in the art is a duplex transceiver with two pre-fabricated conventional TO-can""s that are soldered with bent leads onto the printed transceiver board. The bent leads impose resistance and capacitance onto the system, and reduce with their free lengths the achievable alignment precision.
The support panel has to be mounted on the transceiver board in indirect connection with the TO-cans, which reduces the achievable stiffness. The whole packaging consists mainly of a bulky, one directional assembly on the transceiver board.
U.S. Pat. No. 4,461,537 discloses a fiber optic connector assembly for first generation fiber optics with high signal levels and low bandwidth. The signal conversion is accomplished without secondary circuitry. An optical cable end has a cylindrical plug with shoulders that snap in circularly arranged hooks of a connector housing. A central element of the connector features a circular cavity with the embedded lens, against which the very end of the fiber optic comes to rest. The central element has solder pins for electrical and mechanical connection with a circuit board. The central element has two small interlocking hooks that snap into corresponding slots of the connector housing. The stiffness requirements of the connector housing do not allow sufficiently interlocking noses. The connector housing has therefore additional snap fingers that fit into corresponding holes of the circuit board and secure the assembly.
The reliability of the assembly depends on the accuracy of shape and position of the corresponding holes of the mounting site and create an external quality risk for the fiber-optic connector assembly.
U.S. Pat. No. 4,767,179 discloses an improvement of the patent described above. The fiber optic connector assembly is extended to the application of a duplex transceiver with an independent emitter and receiver station within one housing. The external quality risk as described above is also resolved by adding a bottom board to the assembly where the snap fingers of the connector housing engage.
U.S. Pat. No. 4,985,805 discloses a device for the cooling of optoelectronic components by the use of a flange joint. The patent discloses a massive constructed device with a multitude of three-dimensional mounted components for heavy duty applications. The constructive afford of the design with its space consuming components do not allow the utilization within regular computers.
U.S. Pat. No. 5,280,191 discloses a packaging for pairs of optical devices having thermal dissipation means. The patent discloses a design of a duplex transceiver with secondary circuitry and a heat sink for cooling.
Two optical subassemblies are placed in a receptacle. The POS is integrated together with the SEC on the transceiver board. As a result, the receiving and emitting light beams must be redirected over 90 degrees between the POS and the optical cable end. This is accomplished by an additional bent fiber optic segment, which results in unfavorable optical attenuation and sensitive assembly procedures.
The heat sink is a sheet metal part, which provides only flat areas with low thermal convection.
U.S. Pat. No. 5,513,073 discloses an optical device heat spreader and thermal isolation apparatus. In this duplex transceiver, the POS are connected to a heat spreader card, which is thermally isolated from the transceiver board. A flexible cable string connects the POS with the SEC.
The heat spreading card is a flat sheet metal piece with low thermal convection in a distant assembly position to the transceiver board. The flexible cable string must cross over an edge of the flat sheet metal piece and bridge the distance to the SEC, which is placed in an inner area of the transceiver board. As a result, the flexible cable string has a significant length with unfavorable resistance and capacitance.
U.S. Pat. Nos. 5,420,954 and 5,631,988 disclose a parallel optical interconnect. The SEC and a multiple POS are monolithically grown on a substrate. Two guiding pins are placed in corresponding holes of the substrate lateral to the multiple POS and align intermediate beam guiding elements and a receptacle correspondingly to the multiple POS. The patents represent a miniaturization design, where mechanical alignment features are placed on the substrate itself. Consequently, the involved mechanical parts like the guiding pins, the intermediate beam guiding elements and the receptacle are relatively small and fragile. The direction of receiving and emitting beams is also perpendicular to the transceiver board.
The substrate is placed on the transceiver board and has wire connections to solder pins protruding from the bottom of the transceiver board. The design provides no cooling features and is therefore only useful for low energetic light beam signaling where the thermal load in the circuitry remains low. This is a further limitation that allows an implementation only for short distance communication.
The intermediate beam guiding element adds an additional optical transition in the signal path that unfavorably attenuates the passing optical signals.
U.S. Pat. No. 5,611,013 discloses an optical miniature capsule for a multi channel transceiver. A multiple POS is directly mounted to a front surface of an adapter block with two lateral aligning holes that receive guiding pins of a corresponding optical cable plug. The adapter block is placed on the transceiver board. The front surface is oriented perpendicular to the transceiver board. Bonding wires connect the multiple POS to conductive leads that are bent over the front edge of an attachment face of the adapter block. The attachment face is soldered together with the embedded lead extensions onto corresponding leads of the transceiver board. The corresponding leads reach close to the SEC in the center of the transceiver board. Secondary wires bridge from the corresponding leads to terminals of the SEC, which is a monolithically grown semiconductor. The assembly formed thereby is encapsulated such that only soldering leads stretch lateral off the apparatus.
The conductive path between the multiple POS and the SEC is relatively long with unfavorable resistance and capacitance. The multiple POS is in an exposed position where it can be easily damaged by the guiding pins.
U.S. Pat. No. 5,574,814 discloses a parallel optical transceiver link for a multi-channel FOT. A transceiver board carries the SEC, which is connected with bonded wires to the multiple POS. The POS is protected by a sapphire window. A box like housing is built in a first assembly direction on top of the transceiver board and holds two perpendicular alignment pins, which define a second assembly direction for the receptacle and a number of POS related fixtures.
As a result, the receptacle is connected to the transceiver board via a number of intermediate housing elements, which reduce the mechanical strength and stiffness of the transceiver link.
Since the wire bonding between SEC and multiple POS needs to be performed at an early stage it is difficult to assemble all the fixtures and housing parts without damaging the wire bonding.
U.S. Pat. No. 5,879,173 discloses a removable transceiver module and receptacle for a duplex transceiver. The patent discloses a number of design variations to encapsulate a generic POS/SEC subassembly. Latch and socket combinations make the transceiver module removable.
The patent does not disclose particular packaging improvements of the POS/SEC subassembly. Thermal loads in the transceiver module are not drained either.
The various techniques for optical data transmission make it difficult for a manufacturer to develop efficient fabrication techniques for all of them. For instance time division multiplexing, wavelength division multiplexing, single channel transmission, duplex transmission or multi-channel transmission require separate component designs to adjust to the differing needs for focusing, optoelectronic processing, secondary signal processing and eventual cooling. In addition, the transceiver boards need to provide differing processing operations, which are not necessary related to the utilized optical data transmission technique. As a result, a number of transceiver boards performing different processing operations must be interchangeably compatible with a number of varyingly designed POS components.
Therefore, there exists a need for a simple modular building design for interchangeable components of a optical transceiver.
With increasing processing capacity the optoelectronic circuitry becomes more sensitive to electromagnetic fields imposed by adjacent circuitry. For purposes of miniaturization it is at the same time desirable to have independently operating optoelectronic circuitry in close proximity. Therefore, there exists a need to incorporate magnet shields between adjacent optoelectronic circuitry within a transceiver assembly.
Accordingly, it is a primary object of the present invention to provide a modular building design for a fiber-optic transceiver that is simple and cost effective to fabricate.
It is a further object of the present invention to provide a modular building design for a fiber-optic transceiver that can be utilized for either a duplex or a multi-channel transceiver.
It is a further object of the present invention to provide a modular building design for a fiber optic transceiver that can incorporate faraday shield modules to electromagnetically insulate processing circuitry.
The current invention discloses a modular building design for optical duplex or multi-channel transceivers. The modular building concept includes mainly of three elements: first, a subassembly stack assembled in a first assembly direction; second, a transceiver board being electrically connected to the subassembly; and third a housing providing mechanical support for the electrical connection of the subassembly to the transceiver board and for a cable plug of a connected fiber cable.
The subassembly includes out of interchangeable building modules that allow different configurations with a minimum of fabrication effort. The building modules that require precise alignment to perform their dedicated function are designed with corresponding alignment features such that they can be aligned to each other and stacked in a direction of the traveling beam signals. The stacking direction defines a first assembly orientation.
The modules perform specialized functions such as precision alignment of the cable plug, focusing the light beams, converting beam signals that are received in various numbers of signal strings into electrical signals and vice versa. An optional cooling module drains heat created during the optoelectronic processing.
The individual modules are preferably held together by an encapsulating housing.
The transceiver board is a printed circuit board that carries various integrated circuits (IC) and connects them via conductive leads to perform designated logical operations. The transceiver board is an intermediate link between the optical processing modules and the main board upon which the optical transceiver is mounted on. Two physically differing designs of transceiver boards are available. The first design has laterally extended soldering pins that form a single solder pin array on the main board. The transceiver board is thereby positioned in perpendicular orientation to the main data communication board. This first design concept is preferably used in combination with low capacity optical processing modules such as optical duplex transceivers. The subassembly is preferably solder bonded with the transceiver board.
A second design has at least two solder pin arrays with the solder pins extending perpendicularly from the transceiver board. The two solder pin arrays provide a high number of electrical contacts and are sufficiently separated to define a two dimensional physical connection with the main board. The transceiver board is in parallel orientation to the main data communication board and has on the end of the optical cable a flexible cable band attached. This flexible cable band provides a high number of electrical connections to the subassembly. The second design is used in combination with high capacity optical processing modules such as optical multi-channel transceivers.
There are two main embodiments for the invention. The first housing design has a closed box structure with an opening on the side of the optical cable that forms the receptacle. The transceiver board forms together with the subassembly a rigid core unit and is preferably held inside the housing by snap fingers.
In the final assembly of the optical transceiver the single solder pin array extends into the middle of the bottom face of the housing. Two additional solder pins on each front corner of the bottom face are anchored in the housing and form together with the single solder pin array a two dimensional mechanical connection with the main data communication board. The perpendicular orientation of the transceiver board allows the first housing design to be narrow so that a relatively high number of them can be placed on the edge of the main data communication board.
The second housing design has a stepped shape with a high front half and a shallow back half. The step between the high front ceiling and the shallow back ceiling has a second opening where the heat sink module reaches through so that it is accessible for a cooling air stream. The transceiver board is embedded parallel to the bottom face of the housing with two solder pin arrays reaching there through.
The flexible subassembly is held independently against internal shoulders of the housing with snap fingers, which oppose the flex bias of the cable band. In both housing designs the opening of the housing has an articulated contour that corresponds to that of a cable plug and provides mechanical support for the optical cable connection.
The housing is composed of a plastic material and is preferably molded. The first and second housing designs have simple and very similar shapes that can be economically fabricated. The interlocking of the housing directly with the cable plug and its direct connection with the main data communication board releases the subassembly and the transceiver board from any mechanical loads peripherally imposed via the fiber cable.
The stacking direction of the subassembly corresponds with the fabrication directions of the building modules, which allows simple and economic fabrication.
The interchangeable modular device of the invention can optionally incorporate a faraday module preferably made of copper material. The faraday module provides enclosed cavities in corresponding shape and position to the individual optoelectronic circuitry of a multi-channel transceiver, which rises above the main plain of the optoelectronic module.